The invention relates to an injection molding machine comprising a substantially C-shaped machine frame, on the one limb of which is mounted a stationary mold mounting plate and on the other limb of which is mounted a closing mechanism for driving a movable mold mounting plate, wherein the free ends of the limbs of the machine frame, which ends are not connected by beam members, deform under the influence of the closing force which occurs during the closing operation, and wherein at least one of the mold mounting plates and/or an end plate carrying the closing mechanism are respectively supported against the closing force at their upper and lower edges.
In arrangements of that kind, the purpose of the upper support for the plates is to permit pivotal movement of the plate with respect to the machine frame when the associated limb of the frame pivots outwardly. In that case the upper support can be in the form of a conventional pivot provided with bearing trunnions (see DE 44 20 639 C1), in the form of rolling bearings (see WO 97/07961) or in the form of a deformable holding element (see EP 0 789 648 B1). If, when the limbs of the frame spread open, the ends of the limb are turned inwardly by virtue of the suitable arrangement of a slot in the limb of the frame, the plates can also be rigidly connected to the frame and nonetheless retain their vertical position if the frame deforms under the closing force.
So that the mold mounting plates in the described apparatuses can remain in their vertical position and thus parallel to each other in spite of expansion of the C-frame due to the closing force, it is necessary for the lower edge of the plates to be displaced by a precisely defined distance. In the case of machines with two pivotably arranged plates the displacement of the lower edge must precisely correspond to that of the upper edge. In the case of machines with a single, centrally arranged pivot, as are described in EP 0 311 133, the pivotal movement of the lower edge of the movable mold mounting plate must correspond to the pivotal movement of the mold mounting plate which is fixedly connected to the associated limb of the frame. In order to resolve that problem, DE 44 20 639 C1 proposes the use of two pivotably mounted pressure bars which extend in the longitudinal direction of the machine. For example WO 97/07961 discloses the connection of the pivotable plates by means of lower tie beam members. the longitudinal direction of the machine. For example WO 97/07961 discloses the connection of the pivotable plates by means of lower tie beam members.
Deflection of the limbs of the frame of the machine in the region of the upper pivotal mounting of the plates is to be attributed on the one hand to the pivotal movement of the limb generally and on the other hand to bending and warping thereof. That deformation is not to be correspondingly reproduced either by that of tensile or pressure bars or even more by that of pressure pads or cushions.
In accordance with the invention in comparison it has been possible to provide a lower support whose deformation under the closing force, even in relation to closing forces of different magnitudes, respectively corresponds to the desired value. That is achieved in that the lower support of the mold mounting plate(s) or the end plate respectively is formed by a bending pin which extends transversely with respect to the longitudinal direction of the machine.